It is required that efficiency of a thermal power plant be raised due to recent years demands for economizing the use of fossile fuels, reduction in carbon dioxide emissions, and the like for measures against global warming. In order to raise the efficiency of the thermal power plant, its operations at a higher steam temperature is necessary. The main steam temperature of a conventional boiler for power generation is, at most, about 600° C. even in the case of an ultra supercritical pressure steam power plant, however, a plan is under progress to raise the main steam temperature to 650° C. and further up to a level exceeding 700° C. In the conventional case where a boiler is operated at the main steam temperature of about 600° C., as a material for a large diameter thick-walled tube such as a boiler tube and piping, heat resistant ferritic steel has been used. This is because the heat resistant ferritic steel has the merit of having excellent high temperature strength of up to about 600° C. and a small thermal expansion coefficient and of being comparatively low-priced. However, in the case of not lower than 650° C., the heat resistant ferritic steel is lacking in high temperature strength and oxidation resistance property. Thus, austenitic stainless steel having more excellent high temperature strength and higher oxidation resistance has been proposed to use (cf. JP-A-2004-3000).